Once you open up cararra (the brown cube with a C on it), go to file >new >new empty doc. From here, go to insert > infinite plane. This creates sort of a floor. On the right hand side of the screen, there should be a tab labeled as "motion". Click on it and it opens up a place where you can change the coordinates of the plane.
After you move the plane, click on the blue tab on the left hand side of the screen. Pull it out and look at the different shaders. Look under the category of interior, choose one and drag it onto the plane. I prefer the vase texture. Once you do this, click on insert again, and choose cube.
Once again, choose the motion tab and change the size of the x, y and z. red is x, green is y and blue is z. Change the size of the x to 7, y to 15 and z to 1. After you do this, insert 4 more cubes.
Change the size of each of these cubes. x to 1, y to 1 and z to 10. Move the table legs however you want under the table.
To change the view of what you're looking at, there are 4 icons on the left side of the screen. Each icon has 4 different arrows. The first 3 icons are tracking views. If you click on any of them and click on your scene, you can move the scene around. The 4th icon is the dolly. Play around with all of them for a while so you can get a feel for them. All of these are very useful.
Once you have all of the table legs where you want them, shift click on each piece in your scene and hit apple g. this groups all of the pieces together so when you move the table around, the pieces stay in tact. Click on the drop down arrow on the right hand side of the screen, under the word "Group". You have to shade each piece separately. Click on each piece and select another shader. After you shade each piece, click apple r. this will render the scene. If you like what you see, you can save the product.
This is what I got:

Once you get used to this program and start using it a lot, you can make things like this that I did in my 3-d class: